In order to detect a touch operation on an operation surface such as a display, a variety of touch input devices, each provided with a capacitance sensor, have hitherto been devised. The capacitance sensor is typically made up of a dielectric film disposed in the vicinity of the operation surface and a plurality of electrodes formed on the surface of the dielectric film. In the capacitance sensor, a touch operation is performed on the operation surface to bring a change in electrical field in the vicinity of the operation surface, and thereby bring a change in electrostatic capacitance between the electrodes. Thus, in touch-operation detection processing, a capacitance of the capacitance sensor has regularly been detected as a reference value (hereinafter referred to as a reference capacitance), and a touch operation has been detected based on a variation of an electrostatic capacitance detected from the capacitance sensor (hereinafter referred to as a detected capacitance) from the reference value.
Further, in some cases, the conventional touch input devices have been made up of a deformation sensor in order to detect an operation to deform the operation surface (hereinafter referred to as a deformation operation), such as bending, twisting, and pushing of the operation surface, in addition to the touch operation (e.g., see WO2013/122070).